Telegraph exchange system



Jan., 14, 1941. F, J. SINGER TELEGRAPH EXCHANGE SYSTEM Filed July 5l, 1937 4 Sheets-Sheet 1 @www ,WMM l v mii vak VVE/V70@ By FJ. .SM/GER )VMM Jan. 14, 1941. F. J. SINGER' TELEGRAPH EXCHANGE SYSTEM Filed July 5l, 1957 4 Sl'xeelzs-Sheetl 2 bww,

/m/ENTOR FJ. S//VGER Jan. 14, 1941. F. J. SINGER TELEGRAPH EXCHANGE SYSTEM Filed July 3l, 1957 4 Sheets-Sheet 3 /N/E/V TOR By F J. .S/NGR 3mm TTORNEV v. Gfx

Jan. 14, 1941.

F. J. SINGERv TELEGRAPH EXCHANGE SYSTEM 4 Sheets-'Sheea 4 File'd July 3l, 1937 ibm.

f.- J. SNGER @y 6MM ATTORA/gy Patented Jan. 14, 1941 UNITED STATES ATENT OFFICE TELEGRAPH EXCHANGE SYSTEM Appiication .l'uly 31, i937, Serial No. 156,684

54 Claims.

rIhis invention relates to telegraph exchange systems generally and more particularly to printing telegraph exchange systems wherein any two of a plurality of subscribers or signaling stations in the same or distant exchange areas can be connected together by switching operations `at a plurality of central interconnecting stations by the straightforward trunking method.

The novel features and principles of making connections of this invention are described herein as applied to a straightforward manual printing telegraph exchange system. The application of these principles is not necessarily limited to suoli an exchange system, but may be applied also by certain adaptations to `mechanical and semimechanical straightforward telegraph or equivalent impulse transmission systems.

The service provided by this telegraph system corresponds in general to straightforward toll telephone exchange system service.

A feature of this invention` is the arrangement of the straightforward circuits to provide through supervision.

A further feature of this invention is the 0peration of the facilities interconnecting the origihating, herein called outwardf and completing, herein called inwardj toll central stations, through intermediate, herein called throughj toll central stations when required, and including the calling portion of the outward central cnice cord and the answeringportion of the inward central station cord on a full duplexbasis.

A further feature of this invention is` the maintenance at all times while a connection is established, between an outward and inward toll central station, involving through central stations when required of one independent channel in each direction, over which both supervisory and communication signals are transmitted on a full duplex basis through `the interconnecting facilities including the portions of the cords mentioned in the foregoing paragraph.

A further feature of this inventionis theextension of the full duplex central station interconnecting facilities abovementioned to local sta tions on a half-duplex basis.

A further feature of this invention is the arrangement whereby supervisory signals, indicating the progress of the `call and control of ringing, recall and disconnect arelocalized in the cord circuit of the outward toll central station.

A further feature'of this invention is .that disconnectl signals to the through and ,inward operators are controlled by the outwardoperator.

im A further feature of this invention is an arrangement whereby all supervisory signals originated by the called and calling subscribers appear only in the outward board.

A further feature of this invention is an arrangement whereby the outward operator can send recall signals to the inward operator.

A further feature of this invention is `an arrangement whereby identical cord circuits, that is to say, circuits similar in every respect to those l used in the through central station for extending a toll call are used at the inward toll central station and vice-versa.

A further feature of this invention is an arrangement whereby the cord used in the outward toll central ofhce to answer a call may be used either to extend a toll call or to complete a call to a local subscriber and the supervisory features in the cord at the outward toll central station are essentially the same in either instance.

A further feature of this invention is thatall subscriber-to-subscriber communication and all signals necessary to the establishing of a connection between two subscribers stations as well Vas break, recall and disconnect signals are transmitted over the telegraph facilities in the system without the aid of call circuits or order wires or other `auxiliary facilities.

A further feature of the invention is the pro- Vision of equipment for increasing the speed with which break, recall and disconnect signals are transmitted over the system.

A further feature of the invention is the location of the apparatus responsive to break signals in the cord circuits of the outward and inward toll offices, respectively, and their disposition in such manner that break signals do not interfere with the full duplex operation of the facilities interconnecting the outward and inward toll ofces, including the calling portion of the outward cord and the answering portion of the inward cord.

A'further feature of the invention is the limited participation of through and inward toll central station operators in a call. Their participation is restricted to answering Vthe toll line signals, extending the call, and disconnecting and, Vin the case of the inward toll operator, answering recall, all in response to supervisory signals and information from the outward toll operator who alone is concerned with subscriber signals.

A further feature of this invention is a means whereby an outward operator may start an unattended called station motor and have an indication when the station has `been started.

A further feature of this invention is that code signaling devices to indicate various line conditions are located at each central station to facilitate operation by reducing operating time.

A further feature of this invention is that each end of each interoflice trunk is arranged to automatically signal the operator when a cord is removed from a trunk in error.

A further feature of this invention is that if any cord is removed from any trunk in error, the operator, upon noting the error signal, may reinsert the cord removed in error in the jack without losing the connection.

A further feature of this invention is that at the completion of a call a connection involving one or more through boards will be automatically broken down when the operator at the outward board removes the completing cord from the trunk jack regardless of whether the cords at the through and inward boards are removed from the respective trunk jacks at these officers. Furthermore, a visual indication is registered in these cords and remains until the operators pull down. The trunks may therefore be used for new calls regardless of when the inward and through operators act on the disconnect signals.

A further feature of this invention is the complete provision of guarded busy intervals on the trunks, which prevent an outward operator from completing to a trunk until both ends are prepared to receive the call.

The invention has been illustrated in the accompanying drawings.

A diagram, Fig. 1, on page 1 shows how Figs. 2 to 6 comprising the circuit arrangements of this invention are disposed with relation to each other.

Fig. 1A shows in block form an elaboration of the diagram, Fig. 1, to include plug and jack symbols to convey the figure relationships more graphically. The indicated connections are arranged from left to right in sequence of operation. The top line of this figure shows a telegraph toll connection involving one through toll central station. The invention, however, is not limited to one such through toll central station but may be, and in practice quite frequently will be, extended through a number of such stations.

The teletypewriter subscriber station and busyback symbols in the lower portions of Fig. 1A

, cate that connections may be made to a source of tus and wiring shown at the right is located at the outward central station. The two points are interconnected by the subscribers loop. The subscribers station portion of the circuit includes apparatus and wiring for unattended as well as attended operation. It is to be understood that the station arrangement may be simplified by eliminating the apparatus and wiring for unattended service when this feature is not required.

Fig. 3 shows the cord circuit used at the originating central station. The left-hand portion in general is used in association with the subscribers line, Fig. 2. The right-hand portion in general is used in extending a toll call through a trunk, Fig. 4, or it may be used to complete a local call directly to a called subscribers line in which case the right-hand portion would be used with a second Fig. 2.

A central station operators printer circuit, common to all the cords at an operators position and selectively connected to and disconnected from a particular cord, through the operation of the cord typing key, is shown at the bottom of Fig. 3.

Fig. 4 shows the trunk circuit used on calls other than local, for interconnecting the various central stations. The circuit may be considered as comprising two identical units. The left-hand portion is located at one ol`ce and the righthand portion at another connecting oflice. The circuit shows two full duplex telegraph line repeaters, one at each oiiice. A single wire groundreturn circuit is shown interconnecting the two full duplex telegraph line repeaters. It is understood that this is typical, as the invention is not so limited, but will function on all types of full duplex telegraph circuits, including carrier telegraph circuits. It is also understood that, although only one section of line facility is shown, there may be two or more in tandem made up of direct current or carrier full duplex facilities.

Fig. 5 shows a universal toll cord circuit. It may be used for two purposes: First, at an intermediate toll central station for extending a toll call in conjunction with two Figs. 4, one on each end of the cord second, at an inward toll central station for completing a call to a called subscribers line in conjunction with one Fig. 4 on one end of the cord and one Fig. 2 on the other end.

In Fig. 5 1s shown also, as in Fig. 3, a central station operators position printer circuit, common to all the cords at an operators position and arranged to be selectively connected to or disconnected from a particular cord through the operation of the cord typing key.

Fig. 6 shows the arrangement whereby busyback, reorder and no-circuit signals may be sent back over the circuit to indicate these conditions at boards to which the call has been extended. Since the subscribers printers and the printers at the various stations are arranged so that they can be directly interconnected over the circuit to pass information by teletypewriter, the circuit shown in Fig. 6 is not necessary to the operation of the system but is used as an operating timesaving device.

The detailed description of the operation of the circuits involved in this invention follows:

1. BUILT-UP CONNECTION WITH ONE INTERMEDIATE CENTRAL STATION A straightforward toll call will now be described involving the use of an outward board, a through board and an inward board. Although but one through board is considered in this con- `arid functionngias described herein for the case involving but one through board.

A. Calling subscribercalls--Fg. 2

To signal an operator at an outward board, the calling .subscriber closes the power switch at the subscriberis station, whereupon `the 4associated .station line lamps inthe multiple at the outward the station through the power switch make conltact, starting-the motor. Closing the switch also supplies alternating current from the same source vthrough resistance |20, `relay ||8 winding, armatureand make contact ofthe power switch, to

the alternating current source. Relay ||8 operates, removing ground from the ring ofthe sub- `scribers-loop at its upper armature and back contact-and closing-the loop through the same arma- `ture and front contact.

The station ringer is short-circuited. Normal current flows through the loop which maybe traced from positive battery, resistance lll, upper back contact and armature relay |03, uupper winding relay |I, resistance upper front contact and armature `relay ||0,`teletypewriter contacts, teletypewriter `magnet |00, break-key |09, resistance ||2, lower `inner armature and back contact relay |03, break contact relay |02, resistance ||3 to ground. At

`thecentral office, differential relay |0| operates since current passes through its upper winding. Operation of relay |0| ground through armature and front contact relay |0l, winding relay |02, lower outer'back contact and armature relay |03 to negative battery. Relay |02 operates and lamp |05 lights. Night alarm relay |00 operates.

A1. Calling subscriber abandons caZZ-Fia 2 lTo abandon a call, the calling subscriber opens `the power switch at the subscribers station, ex-

tinguishing `theline lamp at the outward board and restoring the circuit to normal. Reference to Fig. 2 will show the opera-tion in detail.

The power switch at the subscribers station which has been operated to close the right-hand make contact is now reoperated to its normal position. The circuit from the power source for the operation of the teletypewriter motor and relay H3 is broken. The teletypewriter motor stops. Release of relay ||8 breaks the circuit loop and grounds the ring at its upper armature. The circuit through the upper winding oi relay |0| is broken and it releases. The circuit through relay |02 is broken when relay |0| releases. Relay |02 releases. Lamp |05 is extinguished and relay |06 is released.

B. Outward operator answers-Figs. 2 and 3 Prior to answering the operator awaits a call by operating a typing key T, associated with an idle cord to associate the position printer with that cord. She plugs her answering cord into the jack associated with the lighted subscribers line lamp, extinguishing the lamp. The operator then communicates with the calling subscriber.

The detailed functioning of the circuit may be understood from reference to Figs. 2 and 3,

closes a circuit from `lay l 302 operates.

relay `2 I3.

` fnFig. y3, the :typing .key rT, is operated to its :upper contact. :Relay `205 operates from ground `through :the -key armature and upper contact, Vwinding relay 205 :to battery,.connecting the op- .erators position circuit to the cord. The transf `missionfcircuit is open, however, since relays 204 `and2|`3 are knot operated. Relay 30| is on its S contact under control of current through its lower winding. Relay winding 302 is short-circuited `and theteletypewriter magnet 303 is closed, pre- Aventing the teletypewriter mechanism from spinning Since the transmission circuit is open, operating the teletypewriter keyboard contacts has no effect on the mechanism.

The operator inserts the answering cord plug 242 -intofthestation line jack |04 of Fig. 2, to answer'the call. Relays 20| and 202 in the answering `cordand relay |03 in the station line circuit are connected in'series andfoperate over a circuit from battery through relay 20| winding, lower winding relay 202, sleeve plug 224, sleeve jack |04, winding relay |03 to ground. Operation of relay |03 causes relay |02 to release by breaking its circuit at relay |03 lower outer armature and back contact. Relay |02 released, extinguishes line lamp |05 and releases relay |00. Operation of relay |03 connects negative battery through resistance ||4, lower winding of differential relay lili to the loopring conductor, releasing relay 'leased and the ring is not grounded.

'The operation of relay 204 also connects the tip circuit of jack |06 through tip of plug 224, make-before-break contact relay 201|, `top outer make-before-break contact, relay 205, conductor writerkeyboard contacts, break key, upper winding relay 30|, break contact of A portion of splittingkey, Sl?, conductor 230, top inner armature and front contact relay 205, upper winding relay 2|| to positive battery through M contact relay 2|2. The-transmission circuit to the station is therefore closed from negative battery at winding relay-HH to positive battery on the contact relay 2|2. The station and operators teletypewriters are in series. Relay 30| operates` to IVI and re- The operators keyboard is no longer locked and the magnet is under control of relay 30|. The operator and station subscriber l may now communicate.

:Relay 204 also closes a circuit from battery through relay 2|3 winding to ground, operating Relay 204also closes a circuit from ground through its top outer armature and front contact, .through the top winding relay 2|0, to

:positive battery. It also closes a circuit from ground through the same top outer armature and front contact to both windings of relay 2|6, the circuit through the top winding being eX- `tended iromijunction point 23|, over conductor 202, throughthe top winding to positive battery,

vandthe circuit to the bottom windingbeing extended from `junction point 23|, over conductor 220, break contacts ringing key, RA, break con- 45 tacts of C portion of splitting key, SP, teletype- 233, through the top inner armature and back contact of relay 2|'|, through relay 2|6 bottom winding to positive battery. Relay 209 operates when relay 2|| operates to M and connects ground to the bottom winding of relay 2|0. Since the ampere turns through the bottom winding of relay 2|0 are greater than those through its top winding, relay 2|0 operates to M, even though the current through the top winding is in a direction to operate the relay to S. Relay 2|0 operates to M since the ampere turns through its top winding are greater than through the bottom winding.

Operation of relay 2|3 connects ground to the bottom winding of relay 2| I and the middle Winding relay 2|2 through the lef-t and right-hand inner armatures and front contacts, respectively. Relay 2|3 also connects negative battery through its right-hand outer armature and front contact, upper outerI break contacts relay 2|9, upper outer break contacts of relays 2|8 and 2|'I to the top winding relay 2|2. The current through the bottom winding relay 2|| and middle winding relay 2|2 are in a direction to cause these relaysy to operate to S. The currents through the top windings of these relays are in a direction to hold the relays on M and since the effective ampere turns in the top windings are twice as great as those in the bottom winding of relay 2|| and middle winding of relay 2|2, the armatures of relays 2|| and 2|2 remain on their M contacts.

Since the station line circuit is multipled throughout the switchboard, there may be several operators attempting to answer the call when the line lamp lights. The cord relays 202 and 203 in the cord which establishes the connection prevent this from happening. When several cords are plugged in simultaneously, one cord makes the connection and relays 20| and 202 operate as described above. As soon as relay 202 has operated, a low resistance battery shunt through the top winding relay 202 is connected to the sleeve of jack 224. This shunt raises the potential of the sleeve to a value that prevents the 202 relays of other cords from operating. The 20| and 202 relaysI in the cord which has become connected remain operated. In each of the other cords relay 20| only operates and its operation causes relays 203 and 204 to operate. Relay 204 operates over a path from ground, through the armature and front contact relay 20|, through 204 winding to battery. Relay 203 operates from ground through the same armature and front contact relay 20|, through the winding relay 203, back Contact and armature relay 202 to battery. In each of these cords positive battery is therefore connected to the tip circuit through the upper armature and front contact relay 203 and the upper middle armature and front contact relay 204, This potential is equal to that established from the M contact relay 2 |2. The top winding relay 30| in each of these operators position cir cuits is therefore shunted and does not operate to M. Relay 302 does not operate and the keyboard is locked. The positive battery connected to the tip circuit in each of the locked-out cords also shunts out the 30| relay in the operators position circuit of the cord that has obtained the connection and that operator cannot communicate. Since relay 203 is not operated in the cord that establishes the conenction, but is operated in all other cords in the multiple, the position pilot lamps 221 of the interfering cords are lighted. These operators then remove their cords. When all interfering cords have been removed, the remaining .cord can be used by the operator to communicate with the subscriber.

C. Outward operator completes to interofce trunk-Figs. 3 and 4 The outward operator now extends the call by plugging her calling cord into the trunk jack at the outward board. The call cord lamp at the outward board and the trunk lamp at the through-board light and the trunk is made busy at both points. The manner in which this is performed may be seen in detail through reference to Figs'. 3 and 4.

Using the calling cord 226 and with the typing key T operated, the outward operator plugs into the jack 408 of an idle trunk to the distant city containing the through-switchboard or the inward switchboard required for the call. Relays 2|9 and 40| are connected in series over a circuit which may be traced from negative battery, winding of relay 2| 9, sleeve of plug 226, sleeve of jack 408, Winding relay 40| to ground. Relays 2|9 and 40| operate. Operation of relay 40| furnishes ground through its upper outer armature and lower front contact, through the lower winding relay 403 to negative battery. Relay 403 has been held on its S contact by current through its upper winding. With ground connected to its lower Winding, the relay operates to M. This makes the trunk busy and the idle trunk indicating relay circuit, shown by a block, functions to indicate the next idle trunk. The operation of relay 40| also removes connections to the lamp 409 at its top inner armature and back contact and to relay 4|0 at its lower inner armature and back contact, so that neither is energized. The high resistance 4|3 in series with the bottom winding of relay 402 which reduced the current drain for the idle condition, is shunted at the upper outer armature and front contact relay 40| and a circuit is prepared for the operation of relay 405 at the lower outer armature and front Contact relay 40|. Relay 405 does not operate, however, since relay 404 is not operated, as the armatures of relays 406 and 401 are held on their S contacts. This isI so because relays 4| and 4|2 in the trunk from the distant city are on S, or spacing.

Negative battery is applied to the apex of relay 402 through the upper outer break contact relay 404. Current flows through the upper winding relay 402, jack tip 408, plug tip 226, upper outer armature and make contact relay 2| 9, upper outer break contact relay 2|8, upper outer break contact relay 2|'|, upper winding relay 2|2, M contact relay 2I0, M contact relay 2| to positive battery. Relay 2|2 is held on M and relay 402 operates to M since the ampere turns through the upper windings of these relays are twice the value of the ampere turns through the lower windings. When relay 402 operates to M, relay 4| operates to M and at the distant omce relay 4| 2' operates to M. Operation of relay 4|2 to M causes 407 to operate to M over a circuit which may be traced from negative battery through the armature yof relay 4|2, upper winding relay 401 to ground, through the upper outer armature and make contact relay 404. Operation of relay armature 401' to its M contact operates relay 406 over a circuit from ground through relay 401 armature and M contact, bottom winding relay 406' to negative battery.

Operation of relay 400' operates relay 404' over a circuit from ground through the M contact and armature relay 406', through relay 404 winding to battery. Operation of relay 404' causes the multiple line lamps 400 to light over a circuit from battery through the lower armature and upper front contact relay 404', upper inner `armature and back contact relay 405', upper inner armature and back contact relay 40|', through lamp 400' to ground. The idle indicating relay circuit, shown as a box, is also energized from battery through the lower make contacts of relay 404 and the circuit is made busy in the multiple at that point. Night alarm relay 4|0' is operated over a circuit from ground, upper inner armature and front contact relay 404", lower inner back Contact and armature relay 40|', lower outer back Contact and armature relay 405', winding relay 410 to battery, operating the night alarm. When` relay 404 operates the ground applied to the upper winding of relay 401' is momentarily removed and later replaced by a ground through the lower winding of relay 402' and resistance 413'. Relay 401' therefore momentarily operates to S and then returns to M after relay 404-' is fully operated. This does not cause the ground from the M contact of relay 406 to be removed, however, since during the short interval relay 40T' has left its M contact a high surge current flowsin. the lower winding of relay 40B in a direction to hold that relay on M although the current through the upper winding tends to operate it to S.

In the outward cord ground is supplied to the ring of jack 220 from the upper inner armature and back contact relay 404. This ground causes relay 2|5 to operate over' a circuit from` ground, through the upper inner armature and back contact relay 404, ring jack 408, ring plug 220, upper inner armature and front Contact relay 2|0, lower outer armature and back contact relay 214, winding relay 215 to battery. Operation of relay 215 lights lamp 225 over a circuit from ground, through' the lower front contact and armature relay 215, through the lamp iilament, through relay winding 222 to battery. Relay 222 operates, providing an audible signal. The lamp and audible signal furnish an indication to the outward operator that the distant throughoperator has not yet answered the call. Operation of relay 215 operates relay 2|4 from battery through relay 214 lower winding, upper inner armature and front contact relay 215, lower outer back contact and armature relay 214 to the same ground that operated relay 215 onv the upper inner armature of relay 404. The 60 I. P. M. ground used for recall, to be explained herein later, is not applied to the lamp` since relay 215 remains operated.

D. Through-operator answers call-Figs. 3, 4 and 5 The operator at the through-board answers the incoming call by plugging her answering cord into the jack associated with the lighted line lamp, having her typing key 'I' operated. The call cord lamp at the outward board and the line lamps at the `through-board are extinguished. I-Iow this is accomplished may be seen in detail irough reference to Figs. 3, 4 and' 5.

With the typing key operated,` the throughoperator plugs her answering plug 022 into multiple jack 408'. Relays 60|, 002 and 401 operate in series over a circuit from battery, through relay 60| winding, lower Winding relay 15112,` lower outer armature and back contact relay 604, sleeve of plug 022, sleeve of jack 400', winding relay 401' to ground. Operation of relay 40|' releases relay 410' and extinguishes multiple line lamps 400". Relay 405' operates from ground through the lower outer armature and front contact relay 401', winding relay 405', make contact combination and lower armature relay 404' to battery. Relay 405' locks to ground through its lower armature and front contact. Operation of relay 40|' furnishes direct gro-und to relay 002' lower winding by shunting resistance M0 through its upper outer armature and front contact. The current through the bottom winding relay 402' is raised to normal for transmission purposes. Operation of relay 401 also furnishes ground to the bottom winding relay 403' through relay 40|', upper outer armature and lower of the two front contacts. Relay 003' operates to its M contact to hold the trunk busy even though relay 404' subsequently releases, as will be described later under recall and disconnect.

In the cord, operation of relay 00| closes a circuit for the operation of relay 005, from ground, through the front Contact and armature relay 00|, through relay 005 winding, to battery. In case more than one operator answers the call, the 002 relay in the first cord operates but in the other cords relay 603 operates, causing the transmission circuit of all cords to be locked until, all but the rst operator retire in a manner similar to that described for Fig. 3.

Operation of relay 005 operates relays lill and 000. The path for the operation of relay 0H may be traced from battery, through the lower armature and front contact relay 005, relay 0H winding to ground. The path for relay 000 may be traced through the same contact, winding relay 600, to ground, through the upper armature and back contact relay 601. operate, since there is no ground on the ring of plug 022 as relay 404' is operated before the through-operator answers. Operation of relay 0| connects ground to the middle winding relay 000, through relay Gli, left-hand outer make contact and armature. Ground is furnished to the bottom winding relay 010, through the righthand front Contact and armature relay 611. Ground is furnished through the left-hand inner front contact and armature relay 0H to the upper windings relays 015 and 0H. Current through the upper windings of relays @I5 and 0H tends to hold these relays on S but since ground is also applied to the lower windings these relays operate to M. Ground is applied to the bottom winding relay 0H from the left-hand inner make Contact and armature relay 011 through the upper armature and back Contact relay 013. Ground is applied to the lower winding of relay 0|5 through the make contact of relay 0| 0 which has also operated as will be described below. Relay 620 operates from ground, through the armature and right-hand M contact relay 015, through relay 020 winding to battery.

Operation of relay 005 also closes the transmission circuit. This circuit may be traced from negative battery on the M contact relay 412', Fig. 4, top winding relay 401', upper outer armature and front contact relay 404', top winding relay 402', tip of jack 400', tip of plug 022, upper outer front contact and armature relay 005, top winding relay 600, lower outer armature and back contact relay 018', armature and front contact relay 026, armature and M contact relay 010 to positive battery.

Relay E01 does not '40' the ring of plug 226.

Relay 0| 0 is under control of the throughoperators teletypewriter. This transmission circuit may be traced from positive battery, M contact and armature relay 609, break contact relay 0|0, top winding relay 6|0, upper inner front contact and armature relay 6|3, (as relay 6|3 was operated from ground through the upper contact of the typing key) left-hand upper break Contact of the call portion C, of the split key, SP, top winding relay 30|', break key, teletypewriter contacts, right-hand upper break contact of the answering portion, A, of split key, SP, upper outer make-before-break contacts relay 6| 3, upper break contact relay 620 to negative battery.

The transmission circuit is closed through Figs. 4 and 5. On the right side of the cord, Fig. 5, relays 30|', 302', BIS, 626, 6|0 and 6|5 are operated to M. On the left side of the cord relays 601 and 6|1 are operated to M and in the trunk circuit, Fig. 4, relays 402', 403', 406', 401', 6||', 4|2, 4|2, 4||, 401, 400, 403 and 402 are operated to M. Relay 404 operates from ground on relay 406 M contact, through relay 406 armature, relay 404 winding to battery. Operation of relay 404 removes ground at its upper inner armature from the ring of jack 408 and cuts the transmission circuit through from negative battery through the M contact of relay 4|2 through the top winding relay 401, upper outer armature and make contact relay 404 to the apex of relay 402. Relay 405 operates from negative battery on the lower armature and upper front contact relay 404, winding relay 405, lower outer front contact and armature relay 40| to ground. Relay 405 locks to ground through its lower front contact and armature,

In the outward cord, Fig. 3, relay 2|5 now releases since ground has been removed from Relay 2|4 also releases since its locking ground has not yet been applied as relays 22| and 228 have not yet operated. The cord lamp 225 is extinguished, as ground is removed at the lower armature and front contact relay 2 5, indicating to the outward operator that the through-operator has answered.

The outward operator may now type the information required to permit the through-operator to complete the connection to a trunk to the inward board. Operation of the outward keyboard, Fig. 3, causes the current through the top winding relay 30| to be intermittently made and broken. The relay therefore follows these signals and, in turn, operates the magnet 303, causing the teletypewriter to record a copy of the message sent. Relay 302 being slow to release remains operated during this time. In the outward cord, relays 209 and 2| also follow these signals. Relay 2 0, being a slow release relay arranged to release in about one-half second, remains operated. Relay 2|| repeats the signals to the circuit containing the relays 2|2 to 402. Relay 2 |2 does not follow the signals, since when relay 2|| is on M, the top winding of relay 2|2 holds that relay on M, even though the middle winding tends to operate it to Sl. When 2|| is on S, the current through the middle winding of relay 2| 2 has reversed and holds that relay on M. The current through the top and bottom windings is zero since negative battery is applied in the cord and meets negative battery from the M contact of relay 4|2 in Fig. 4. Relay 402, however, follows the signals sent by the outward operator and these signals are also followed by relays 4|| and 4|2'. Relay 401' and relay E09 in Fig. 5 also follow these signals. Relay 406' does not release since it is arranged to remain operated for one second after relay 408 leaves its contact. During normal teletypewriter or break signaling, relay 401 does not leave its contact that long.

In the through cord, relay 000 applies positive and negative battery intermittently to the apex circuit of relay 6|0 and to the loop containing the through-operators teletypewriter. Relay 6|0 does not follow the signals, since when relay 500 is on M, the current through the upper winding of relay 6|0 is sufficiently large to overcome the effect of the current in the lower winding. When relay 009 is on S the current through the upper winding of relay 6| 0 is zero but the current through the lower winding has reversed and 0|0 remains on M. Relay 30| in the position circuit, however, repeats these signals. Magnet 303 follows the signals and the teletypewriter records the message sent by the outward operator. Relay 302' operates and remains operated during this period.

El. Through-operator completes call-Figs. 3, 4 and 5 After the through-operator receives the necessary information from the outward operator, she plugs her calling cord into the interoflice trunk jack to the inward board. The call cord lamp at the outward board and the interoiiice trunk line lamps at the inward board are lighted. The through-operator then releases the cord typing key which removes the position circuit from the through-operators cord. The trunk between the through and inward board is made busy and the trunk between the outward and through board remains busy. How the circuit functions in detail to perform this may be seen on reference to Figs. 3, 4 and 5.

Whenthe completing cord 623 is inserted in jack 408 of the trunk toward the inward board, relays SI2 and 620 in Fig, 5 operate in series with relay 40|, Fig. 4, over a circuit which may be traced from ground, through relay 40| winding,

, sleeve`of jack 408, sleeve of plug 623, winding relay 620, winding relay SI2, lower front contact and armature relay 605 to battery. Relay SI2 operates in this instance, since the resistance of relay 40| winding is low enough in Value to permit such operation. If plug 623 had been connected to a station jack |04, Fig. 2, relay 6|2 would not have operated, since the station sleeve relay |03 has a relatively high resistance.

The operation of relay 6|2 prevents a flashing lamp appearing as a recall signal from the Outward board and also removes the break" feature from the cord by substituting an impedance 629 for the lower winding of relay 600. These features will be described in more detail later.

Since ground is applied to the ring of plug 623 when the through-operator completes the connection, relay 0|9 operates over a circuit from ground, through the upper inner armature and back contact relay 404, ring of jack 408, ring of plug 623, winding relay BIS, lower armature and front contact relay 620 to negative battery. Operation of relay 6|!! causes the transmission circuit toward the inward board to be cut and closed. This circuit may be traced from positive battery through the M contact and armature relay 609, make-before-break contact and armature relay 0|9, upper inner break contact and armature relay 6|3, upper make-before-break contact and armature relay 620, tip of plug 623,

tip of jack 408, Fig. 4, topI winding relay 402,upperl outer break contact of make-before-break combination relay 404 to negative battery. Relay 4M remains released until the inward operator answers since the transmission` circuit from the inward board is in a spacing condition and relays 4% and lill are on their spacing contacts. With the closure of the transmission circuit toward the inward board, relay W2 operates toM and, in turn, relays lll I, M2', dill', M16 and 40d" operate in the same manner as. was described previously for the through-board to light the multiple line lamps 469' and to make the trunk busy at the inward board.

The transmission circuit toward the outward switchboard is opened when relay El 9 operates as relay 6`I8`operates from ground, through the upper front contact and armature relay 6l9 upper winding relay BIB to battery. With relay 548 operated, negative battery is supplied through its lower cuter front contact and armature to the apex of relay 559, and thence through the upper outer armature and front contact relay 685 to the tip of plug 622. This space signal causes relay 402', in Fig. 4, associated with plug G22, to operate to S and relays 4l I and 4I2` in the interoflice trunk toward the outward board to operate to S. In the trunk terminating circuit at the outward board, relay ll'l operates to S and after one second relay ltllli also operates to S. Relay 404 releases and connects ground to the ring circuit of the outward cord, reoperating relay 2l5 and causing the outward completing cord lampto light as previously described. This lighted lamp gives the outward operator an indication that the throughoperator has completed the connection to the inward board.

E2. Through-operator sends busy back, reorder or 11o-circuit signals back to outward operator- Fzgs. 3, 4, 5 and 6 In case the through-operator iinds all trunks to the inward board busy, she will complete to one of the three jacks shown in Fig. 6, depending on the traic circumstances. Busy back, reorder or no-circuit signals will thereupon be transmitted to the outward board to be recorded on the outward position teletypewriter. Reference to Figs. 3, 4, 5 and 6 will show this operation.

Plug 623, Fig. 5, is inserted into either one of the three jacks, busy back, reorder or nocircuit, Fig. 6. Ground is furnished in each instance over the sleeve of the jack to operate relay 625i as heretoiore described. The operation ofA relay 62u closes the cord tip circuit. Relays El2, tls, and l do not operate. Battery interrupted to give the proper code signal by the interrupters in Fig. 6 will be transmitted over the tip of the jack to cause relay Ell) in the cord to repeat this signal through the transmission circuit to the outward board. The outward operator receives the corresponding signal over trunk, Fig. 4, on her teletypewriter in Fig. 3.

The sleeve resistance on` the jacks in Fig. 6 `is relatively high, equivalent to that of relay Mil in Fig. 4. This is the reason that when an inward or through cord plug 6M is connected to it relay SI2 in the cord is not operated. The cord is therefore .arranged to receive either a recall or disconnect signal from` the outward board. As the details of recall and disconnect signal operation will be described in later sections, they will be omitted here.

F. Inward operator anszvers call-Figs. 3, 4 cmd 5 The inward operatoranswers the call incoming to the inward board. To do this., with the cord `typing key T, operated, she inserts her answering cord plug into the jack associated with the lighted line lamp in the interoiiice trunk multiple. The call cord lamp in the outward board and the line lamp in the interoiice trunk multiple at the inward board are extinguished.

The inward cord with the operators teletypewriter equipment and the trunk circuit function for this operation as for the case when the through-operator answered the call incoming tothe through board from the outward ofiice. Reference to Figs. 3, 4 and. 5 will disclose these operations.

At the through oilice the W6 and` Mil relays in the through-inward interoiiice trunk circuit operate to M when the inward operator plugs in to answer. The operation of relay tilt at the through oliice causes relay 4M to operate over a circuit from ground through relay d armature, relay 404 winding to battery. Relay 455 operates from. battery through the lower armature and upper front contact relay 4M, relay 405 winding front Contact and lower outer armature, relay 69|, toI ground. The operation of relay 4M removes ground frcm the ring of jack 408 at its upper inner armature and back contact. This causes relay Elli of the through cord to release :and when relay 6 I B releases` relay 8 l 8 also releases. With relay GIS released, the transmission circuit of the through cord is cut through and the marking signal from the inward board is extended over the trunk to the outward board. In the outward oflice, relays 49'! and M16 again operate to M. Relays 4M and M35 then operate and the call cord lamp at the outward board is again extinguished as previously described. The outward operator, noting this extinguished lamp, then types the number of the called station. This number is received on the teletypewriter at the inward board over a transmission circuit which has been described before up to the through switchboard. Relay 659 in the through switchboard repeats the signal-s to the tip of the call cord and the signals are then repeated to the teletypewriter at the in ward board in a manner similar to that described previously for the case where the outward operator communicated with the through operator.

G1. Inward operator completes to called station Zine-Figs. 3, 4 and 5 The inward operator now makes a tip busy test on the sleeve oi the called station jack and, upon noting that the line is idle, plugs the calling cord into the jack; Thisv makes the station line busy and lights the calling cord lamp at the outward board. The detailed operation` of the circuits to perform these functions may be seen by referring to Figs. 3, 4 and 5.

Before plugging in to the called station jack lull", Fig. 2, of the called subscriber line, the inward operator determines whether or not that line is busy. rThis operation is performed by making a tip busy test with the calling cord plug E23, Fig. 5. If the line is busy, another cord is in the multiple and there is a potential on the sleeve` due to the battery from the sleeve of the answering cord of anA outward cord pair, Fig. 3, or from the sleeve ofthe calling cord of another inward cord, Fig. 5. When the tip test is made, a relay common' to all cords in the position operates if theV line is busy and its operation causes a position busy lamp to light. The relay and lamp are not shown in Fig. 5 but the relay winding is connected to the upper back contact relay E20.

Assuming the line is idle, the inward operator completes the connection by inserting plug 623 into .jack |04 of the called station line. Relays |03, @i2 and 620 are thereby connected in series over a circuit from battery through the bottom armature and front contact relay 605, winding relay SI2, winding relay 620, sleeve plug 623, sleeve jack |04, winding relay |03, to ground. Since relay |03 has a relatively high resistance, there is insuicient current to operate the marginal relay SI2 but relays |03 and 620 operate.

In the station line circuit, operation of relay |03 causes positive battery to be removed from the tip of the loop at its upper armature and back contact, and connects negative battery through the lower winding of relay IOI, front contact and lower inner armature of relay |03 to ground at the upper armature and break contact of relay H8. Battery is also removed from relay |02 at the lower outer armature and back contact of relay |03 so that relay |02 cannot operate. Relay IOI operates since its lower winding is energized and ground is thereby connected to the ring oi jack |54.

In the inward cord, Fig. 5, operation of relay 620 removes negative battery from the transmission or tip lead at the break contact of the upper make-before-break combination of relay 620 and extends this circuit to an open at the upper make contact of relay II8, at the subscriber station. Since the transmission circuit is -now open and relay 6 I0 operates to S under control of its bottom winding, causing a spacing signal to be applied to the apex of relay 609 over a circuit from negative battery through the upper back contact of relay GIZ, lower winding of relay 609, S contact and armature relay 6I0, front contact and armature relay 626, back contact and lower outer armature relay EIB, to apex circuit relay 609. This spacing signal is sent over the circuit to the distant outward switchboard. Relay 609 remains on its M contact because the currents through its middle and lower windings from negative battery at the S` contact of relay 6|0 are in a direction to hold relay 009 on that contact. At this time the vcurrent through the upper winding of relay 600 is zero. After one-half second the break-limiting relay EI 5 also operates to its S contact and causes relay 026 to release but the operation is ineffective since before this time has elapsed relay GIS operates from battery through the front contact and lower armature relay 620, winding relay 6 I9, ring of plug 623, ring of jack |04 to ground at relay IOI armature. The operation of relay BIS operates relay 6I8 from ground through the front contact and upper inner armature relay 6I9, top winding relay 6I8 to battery. Relay 6I8 remains operated until the called subscriber answers or the cord connection is broken. Operation of relay I 9 transfers the armature of relay 609 tothe tip circuit of plug 623 through its lower armature and front contact for subsequent use when the outward operator rings. Operation of relay 6I8 removes the armature of relay BID from the transmission circuit and connects negative battery to the apex of relay 609, which causes the spacing signal which was started when relay 0I0 operated to S to be continued as a permanent signal. Relay 609 remains on S because current is still applied to its middle winding. Operation of relay 6 |8 also breaks the ground connection from the left-hand inner armature and make contact relay 6I I to the lower winding relay 6I'I. After one and one-eighth seconds, relay 6I'I operates to S, removing the locking circuit through the bottom winding relay EIS so that relay 6|8 is held operated only by its top winding under control of relay GIS.

The spacing signal sent from the apex of relay i500 through the lower make contact of relay GIB in the inward cord causes relay 402 in Fig. 4 at the inward office to operate to S. The signal then operates relays 4| I and 4I2 of the interofce trunk to S and at the through ofce relays 40T, GID, SIG and 402' also operate to S. The signal is then propagated toward the outward oice since relays 4I I and 4I2 in the through outward switchboard interoflice trunk circuit also operate to S. Finally at the outward ofce relay 401 operates to S.

One-half second after relay Siti in the through cord operates to Si the G I 5 relay also operates to S. However, this operation is ineiective since relay SI2 is operated and ground is held on relay 626 through the lower inner make contact of relay 6I2. Relay 02S therefore remains operated and the transmission circuit between the armature of relay 6I0 and the apex of relay 809 is not broken. One second after the 407 relays in Fig. 4 at the through and outward switchboards operates to S, the corresponding 406 relays also operate to S and in turn the 404 and 405 relays release, causing ground to be applied to the ring oi plugs 623 and 226, respectively, at the upper inner armature and back contacts relays 404.

At the through switchboard relays EIS and 6I8 then operate but during the operating time of relay GIS and after it has operated, relay 402 in the trunk terminating circuit toward the outward board remains on S under the influence of current through its lower winding from battery at the M Contact of relay 4|2. After relay 6I8 in the through cord has operated, the windings of relay BII) are no longer in the transmission circuit toward the inward board but the armature of relay 0I!) is also removed from the transmission circuit toward the outward board so the outward switchboard operator can send ringing pulses through the through switchboard without aiecting the permanent spacing signal which is still being transmitted to the outward board. At the outward switchboard the application of ground to the ring of plug 226 causes relay 2| 5 to operate as has been heretofore described. With relay 2I5 operated the cord lamp 225 again lights, indicating to the outward operator that the inwardoperator has completed to the called station line.

It is to be noted that in tracing the spacing signal that was propagated from the inward to.` the outward board, the transmission circuit of the calling station and outward operators teletypewriters was broken for about one second; that is, until relay 404 in Fig. 4 at the outward switchboard released.

Thereafter the circuit was cut and closed from negative battery through the upper break contacts of relay 404 so that the calling subscriber and outward operator could communicate and so that the outward operator had complete control of the transmission circuit toward the called station.

G2. Inward operator sends busy back, reorder or 1ro-circuit signal-Figs. 5 and 6 Facilities per Fig. 6, such as were provided at til) the outward board, are also provided at the in-v ward board in order to inform the outward operator of similar conditions existing at the inward board. The operation of Fig. 6 under these circumstances is similar to` that described under E2.

H. Outward operator rings called stdtzonmFig/s. 2, 3, 4 and 5 To ring the called station the outward operator operates her ringing key, RC, momentarily. The calling cord lamp remains lighted. The detailed operation of the circuits under the circumstances may be observed from references to Figs. 2, 3, 4 and 5.

Upon noting the relighting of lamp 225, Fig. 3, after having ordered the connection to be established to the called station line, the outward operator operates the ring-called-station, RC, key momentarily.

Operation of this key operates relay 221 from ground through the upper left-handl armature and iront contact oi the key, winding relay 22|, iront contact and lower inner armature relay 2l!) to battery. Relay 221 locks from ground i through its lower armature and front contact.

With relay 221 operated, a circuit is prepared for the operation of relay 228, but this relay does not operate until later, as explained below. Operation of the ring-called-station key, RC, also operates relay 218, from ground through the lower armature and front contact of the key through relay 218 winding to battery. Relay 218 locks from battery through its winding, front contact and lower inner armature relay 2i8, iront contact and upper inner armature relay 219, ring or plug 22E to ground through the back Contact and top inner armature relay 404.

With relay 218 operated and locked, relay 228 is prevented from operating. The transmission circuit oi the cord is cut and closed toward the calling station and a circuit is established for the operation of relay 221).

Ringing relay 221) is connected to a machine ringing generator which applies ground to the circuit for two seconds and then opens the circuit ior four seconds. With relay 218 operated, relay 220 remains operated for two seconds out of every cycle of six seconds duration. During the two-second period when relay 220 is operated, a source oi twenty cycles alternating current voltage is applied from ground through the twenty-cycle alternating current source to the `front contact and armature of relay 220, top

inner armature and. front contact relay 218, front contact and top outer armature relay 219 to the tip of plug 222. During the four-second period while 221i is released the positive battery is supplied through the back contact of the relay over the same path to tip of plug 226. Relay 4112, Fig. 4, follows these signals. It sends a series oi d; signals'having a period oi twenty cycles per second for two seconds and then remains on M for four seconds. These signal patterns are transmitted over the line to the through oilice by relays 422, 411 and 412' and in the through cord, Fig. 5, relay 5051 repeats them directly to the next trunk since relay 619 in the through cord is still operated. Relays B and 616 also follow these signals but are ineffective since relays 612 and E13 are also operated.

From the through oince `to the inward office the signals are repeated bythe corresponding relays to those described for the outward through trunk case and are repeated to the called station line by relay 609 of the inward cord. As in the thro-ugh cord relays 616 and 612 follow these signals but these relays are disconnected from their normal circuits so that their operation causes no interference.

As relay 609 transmits the ringing signal pat terns to the tip of the inward cord plug 623, the signals pass over the tip of the station line, through the station ringer to ground. In the station line circuit, relay 191 remains operated since the current through its lower winding is larger in Value than the peak values of the signaling current flowing through its upper winding.

At the outward switchboard the operator may retire from the circuit by releasing the typing key since the called cord lamp 225 acts as a ringing cord lamp and is extinguished when the called subscriber answers.

Il. Called subscriber answers-Figs. 2, 3, 4 and 5 To answer, the called subscriber operates the power switch at the called station to the right. The calling cord lamp at the outward switch is thereupon extinguished. The operation of the circuit in detail may be understood from,refer ence to Figs. 2, 3, 4 and 5.

Operation of the power switch to the right at the called station, Fig. 2, starts the teletypewriter motor and operates relay |13. Operation of relay 118 closes the loop and removes ground from the ring conductor. Relay lill, being a differential relay, releases during the rst foursecond closed period oi the ringing signaling pulse since current now flows from negative battery through its lower winding over the station loop through the upper winding and to positive battery on the M contact of relay iiiid in the inward cord.

Relays B16, El and 626 in the inward cord operate to M and as soon as relay lill releases, relay 619 in the inward cord releases and it in turn causes relay 518 to release. `Release of relay 618 causes relay G11 to reoperate to M and also removes negative battery from the apex oi relay @G9 and replaces it with positive battery from the armature of relay lilil. Relay iilti is operated to M, because relay 629 is marking and current iiows from positive battery through the M Contact of relay Elli), through the upper winding of relay 610 and over the called station loop to negative battery connected to the lower winding of relay 101. The permanent spacing signal which had been applied to the channel toward the outward board before the calling subscriber had answered is, therefore, now replaced by a marking signal. This marking signal causes the relays lli'l and 405 at the through and outward ofces to operate to M and relays 4M and tilt to reoperate. With relay 4M at the through switchboard reoperated, relays 6 l 9 and 618 in the through cord release and the connections to relays 609 and E10 are restored to normal transmitting condition.

With the 464 and 405 relays at the outward switchboard reoperated, ground is removed from the ring of plug 22S and relay 218 releases. Release of relay 218 causes the circuit to relay 22B to be broken at its lower-outer armature and iront contact. Release of relay M8 also connects the transmission circuit from the winding of relay 212 to the tip of plug 226 so that the calling and called subscribers can communicate. The release of relay 218 also operates relay 223, from battery through the lower-outer armature and back co-ntact of relay 2I0, winding relay 228 to the front contact and upper armature of relay 22| to ground. Meanwhile relay 2I5 released since its operating path was bro-ken when the 5 ground was removed from the ring of plug 226 and relay 2lb?, which was also operated, released before its locking path through the now made contact of relay 228 was closed.

The lamp 225, therefore, is extinguished and l0 the circuit is ready for communication to start.

I2. Outward operator starts called station teletypewrz'ter for unattended service To start the teletypewriter at an unattended called station, the ring-called-station key RC, in the outward board is operated for ve seconds. The teletypewriter at the unattended station is started and the calling cord lamp in the outward board is extinguished. Reference to Figs. 2, 3, 4

and 5 will show the operation in detail.

Under H above, ringing the called subscriber for attended called station operation was described in detail. To start a teletypewriter at an unattended station, the ring-called-station key RC in Fig. 3 is operated as was the case for ringing an attended station. In this instance, however, the key is held operated by the outward operation for ve seconds. Relays 2I8 and 220 operate and lock, and ringing is impressed on the subscribers station circuit over the tip lead as described under H in detail, except in this instance relay 220, is held operated during the ve seconds while the key is operated over an obvious circuit, and the ringing is continuous.

The i signals repeated from the 609 relay in Fig. 5 over the tip of the subscribers line pass through alternating-current relay H5 winding, upper armature and back contact relay H8 to ground. Relay I I5 operates, closing a path from 10 the alternating-current source, resistance H9,

relay IIB winding, armature and front contact relay IIE to the alternating-current source.

When the i signal has persisted for five seconds, relay II6, a slow-acting thermal relay, operates. With the operation of relay II6, a path is closed from ground on one side of the alternating-current source through the armature and front contact relay I I6, winding relay II'I, to the r other side of the alternating-current source. .i0

Relay II'l operates and locks over a circuit from the right-hand conductor from the alternatingcurrent source, through the teletypewriter motor control contacts I2I, break contact and armature `f the power switch, lower armature, front contact and winding relay III to the left-hand conductor of the alternating-current source. Operation of relay I I I also closes a path at its upper armature and front contact in parallel with the onen power switch contact, starting the teletypewriter motor and operating relay H8 over obvious circuits. Operation of relay H8 removes the ring ground at its upper armature and back contact and closes the subscribers loop through the same armature and front contact. Relays H5 and IIB release as soon as relay H8 operates since relay winding I I5 is then short-circuited. Relays II'I and H8 remain operated while the station is in operation and until, at the conclusion of the communication, an upper case H character is transmitted, opening the motor control contacts I2I momentarily. This opens the locking path of relay II'I releasing it, which in turn releases relay H8, again opening the subscrlbers loop and grounding the ring, and stops the teletypewriter motor, restoring the circuit to normal.

J. CalZzng and called subscribers communicate- Fz'gs. 2, 3, 4 and 5 The calling and called subscribers are now in position to communicate with each other. Figs. 2, 3, 4 and 5 show the operation in detail.

During normal communication between the calling and called subscribers, marking and spac- 10 ing signals are sent to and fro between the stations. The spacing impulses never exceed a small per cent of one second. The break-limiting relays 2I0 and 6I5 remain on M. Furthermorethe recall relays 2I6 and 6I`I and the trunk 15 relays 406 and 406' all remain on M.

When signals are sent from the calling station, the following relays respond to the signals: Outward cordrelays 209 and 2l I.

Outward-through trunkrelays 402, 4I I, M2 20 and 401'.

Through cord-relay 600.

Through inward trunk-relays 602, III l, M2 and Inward cord-relay 609. 25

When signals are sent from the called station, the following relays respond to these signals: Inward cord-relays 6I0 and GIS.

Inward-through trunk-relays 402', iI I', 2I2 and @01. 30 Through cord-relays 6 I 0 and BIG. Through-outward trunk-relays 402', 4I I', H2

and 401.

Outward cord-relay 2 I 2.

If the called subscriber wishes to break the 35 calling subscriber while the latter is sending, the called subscriber holds his break key |09 operated for about one second. This causes relays 6I0 and 6I6 in the inward cord to operate to S as soon as relay 609 has operated to M. It is to 40 be noted that with relay BID on its S contact a circuit is established from negative battery through the lower Winding of relay 609 to the S contact of relay SID, lower make contact of relay 626, lower break contact of relay 6I8, apex of 45 relay 609, center winding of relay 609, resistance, left make contact of relay 6H to ground. Currents therefore flow through the center and lower windings of relay 600 from the negative battery associated with the spacing contact of relay 6I0. 50 These two windings are connected in an aiding direction and are of sufficient magnitude to hold relay 609 on its M contact, regardless of whether a spacing or marking signal is being received 5 from relay 4I2 in Fig. 4. Relay Bil!) therefore o remains on M as long as the break key |09, at the called station is held operated and relays 6I0 and 6I6 remain on S causing an interrupted space to be sent into the trunk circuit. Relays 402', 4H', M2 and am in the inward-through 6 trunk, relays 6I0 and GIS in the through cord, and relays 402', 4I I', M2 and 401 in the through outward trunk, then operate successively to spacing. The spacing signal finally reaches relay 2I2 in the outward cord and as soon as the calling 65 subscriber sends the next mark signal, relay 2H operates to M and the current through the top winding of relay 2I2 is reduced to zero. Since the current through the middle winding still persists, relay 2I2 operates to S before relay 2H has 70 had time to leave its M contact. With relay 2I2 on S, the calling station loop current is reduced to zero, relay 2H is prevented from operating to S and the calling subscribers sending is broken.

1f the called subscriber holds his break key, las, '15

operated for more than one-half second, the SI relay in the inward oord and possibly also in the through cord will operate to S since ground is removed from its bottom winding when relay GIG releases. This operation in the inward cord will cause the trunk toward the through switchboard to be cut and closed by release of the 626 relay and since this occurs in considerably less than one second after the space signal is started, the 406 relays in the trunk-terminating circuits will not operate to S and there will be no false supervisory signals. If the SI5 relay in the through cord releases, its release will be ineiective since relay 622 is held operated through the lower inner make contact of relay SI2. When the called subscriber releases the break key |09, the transmitting relays in the inward and through cords and trunks restore to marking and relays 6 I6 and SI5 in the inward through cords and relay 626 in the inward cord reoperate and the called subscriber may then send.

When signals are being sent to the calling subscriber, he toomay stop this sending by operating his break key, |29, for more than one-half second. In the outward cord, signals are at this time being repeated by relay 2 I 2, and relay 22S is following these signals. Regardless of whether a marking or spacing signal is being received, when the break key, |09, is operated, the current through the top winding of relay 2II is permanently reduced to zero and when relay 2 I 2 reaches its M contact, the current through the bottom winding of relay 2l I causes it to operate to S. As soon as relay 2 I I reaches S, relay 299 releases and the currents through the bottom and middle windings of relay 212 hold that relay on M, regardless of the current through its top winding. The permanent S signal from relay 2li is therefore propagated over the trunks to the called station.

One-half second after the break key Illil, at the calling station is operated, relay 2in, Fig. 3, opcrates to S and cuts and closes the transmission circuit to the inward board, thereby limiting the break and preventing the 426' trunk relays from operating to S and causing alse supervisory signals.

It is to be noted from the foregoing that the break feature in this complete network is located in the outward and inward cord circuits only and that either teletypewriter or supervisory signals may be sent over the trunks and through the through cord in both directions at the same time without interference. In the through cord the lower winding of relay 609 is open because relay SI2 is operated when a connection is established and the break feature, lower winding of relay 629, is disconnected. It is this full duplex feature of the system that permits the through supervision to be unaffected by the various teletypewriter transmission conditions of the system.

K1. Calling subscriber recalls and outward operator answers recall-Figs. 2 and 3 To recall, the calling subscriber operates the power switch at the subscribers station to the left or off-position and then again tc the right or onposition. The answering cord lamp at the outward board flashes. The operator answers by operating the typing key, which extinguishes the flashing lamp. Reference to Figs. 2 and 3 will show this in detail.

If the calling subscriber for any reason wishes to send a recall signal to the outward operator, it may be done, regardless of whether or not the teletypewriter is receiving a marking signal. In case of trunk failures or troubles of other sorts, the communication signal received at the calling station may be either a marking or spacing signal or a succession of marking and spacing signals. For any of these conditions a momentary operation of the power switch, Fig. 2, to the orf-posi tion, followed by restoration to the on-position will cause a flashing recall signal to be received at the outward cord.

When the power switch is oil, the dierential relay IDI will operate from negative battery through its lower winding, front contact and lower inner armature relay |23, resistance l I2, lower back contact of relay I i8, and upper back contact of relay IIB to ground. When relay lill operates, it applies ground to the ring of jack IEM and plug 224, Fig. 3. Relay 221 operates. With relay 2M operated, relay 228 operates over a circuit from battery through the upper inner armature and front contact relay 2M, front contact and upper outer armature and front contact relay 2M, iront contact and upper outer armature relay 221 to the same ground over the ring circuit. When relay 221 operates, negative battery is furnished through its lower outer armature and front contact to the transmission lead at the winding oi relay 2li. Relay 2li operates to its M contact and in turn reoperates relay 29. The length of spacing signal sent to the trunk by relay 2l I when the power switch at the station is off, s therefore relatively short, being the sum of the operate times of relays IElI and 207. This period is considerabiy less than one-half second and the break-limiting relay 2li! remains on its M contact. The operation of relay 221 also applies ground to cord lamp 223 and the common night alarm relay 222 over a circuit from ground through the front contact and lower inner armature relay 221, lament lamp 223, relay winding 222 to battery. Lamp 223 therefore lights and the night alarm sounds.

After the short period required at the station to release and reoperate the power switch, relay IBI releases again and then relay 22? releases. Relay 208 remains operated, however, since it is locked to ground over a circuit from battery through top winding relay 208, upper armature and front contact relay 228, lower armature and front contact relay 205 to ground. A source oi interrupted ground is therefore applied to lamp 223 and relay 222 as soon as relay 2M releases over a circuit from ground through the interrupter, lower inner armature and front Contact relay 228, back contact and lower inner armature relay ZilI, iilament lamp 223, winding relay 222 to battery. The lamp therefore hashes at a 6o I. P. M. rate indicating a recall.

The outward operator answers the recall by operating the typing key, T, to its upper contact, operating relay 225. During the travel time of the relay ground is momentarily removed from the locking winding of relay 22B at the lower armature of relay 205 and relay 228 is released. The operator may then challenge and communicate with the calling subscriber. If a permanent space is being received from the trunk, the operator may operate the position split key to close the circuit and to permit the communication.

If during the time the position circuit is connected to the cord, such as when a toll connec tion is being established, the calling subscriber recalls, the station and outward cord circuits function in the same manner as described above. In this case, however, relay 2ll8 is locked operated from ground through the lower armature and front contact 'of relay 2&5. To release this circuit and extinguish the lamp the operator restores the typing key momentarily, again releasing and unlocking relay 296. After reopcrating the key to connect the position printer again to the cord the operator challenges the subscriber.

K2. Called subscriber recalls and outward operator answers recall-Jigs. 2, 3, 4, and 5 To recall, the called subscriber operates the power switch to the left or off-position and then again to the right or on-position. The calling cord lamp at the outward board hashes, the operator answers by operating the typing key, T, which extinguishes the dashing lamp. Reference to Figs. 2, 3, 4 and 5 will show the operation in detail.

If, after a connection has been established in accordance with the plan described in A to J above, the called subscriber wishes to recall the operator, he may do so by momentarily releasing the power switch in the same manner as described for the calling station in Kl above. This recall signal is translated in the inward cord, Fig. 5, to a code signal, 11/8 seconds timed open, by relay Sil, and this signal is transmitted over the interoidce trunks to the outward switchboard where it causes lamp 225 to flash and relay 222 to operate. This recall signal does not appear as a lamp signal at the inward and through switchboards and may be transmitted even though the calling station is transmitting a marking or spacing teletypewriter signal, a break signal, or a recall or disconnect signal. Referring to Fig. 2, relay lill is momentarily operated and released as heretofore described, causing ground to be applied momentarily to the ring of plug 623, Fig. 5. Relay @I9 operates and its operation causes relay GIB to operate through its top winding. When relay Gia operates, negative battery is applied to the apex of relay 6&9 at the lower outer armature and front contact, and the spacing signal is propagated over the trunks to the outward board in the same manner as described under G above. This spacing signal persists until relay I'I releases. Relay 'oIi remains operated for a short period, that is, during the release time of the station power switch. This time is sulicient to allow relay 668 to operate. When relay E58 operates, its lower winding is energized through its bottom inner armature and front contact, relay GI'I armature and M Contact to ground at the lower inner armature and back contact of relay SI2, and is held operated over this path even though relay QSIS releases. With relay @I8 operated, ground from the left-hand inner armature and front contact of relay 6H is removed from the bottom winding of relay 6H and after condenser a2? is charged from positive battery through the lower winding, the current dies down to a low enough Value to permit the current through the top winding to operate relay iI'l to S. As soon as relay EI'I operates to S, relay @I3 releases since its holding path, above described, is open. Release of relay (lS again closes the transmission path toward the outward board at its lower outer armature and back contact to positive battery from the M contact of relay SIB.

At the through and outward offices, relay 43% in the trunk circuits toward the inward board are slow-release relays, but their time of release is sufiiciently less than that of relay 6I? to insure that the respective 404 and '455 relays in the trunk terminating circuits and relays EIS and IBIS in the through cord, and relays BIE and 2M in the outward cord operate.

When the spacing signal from the inward cord is started through the through cord, relays GIO and Sl in the through cord release. The release of relay GII) causes negative or spacing battery to be applied to the apex of relay 639 and the signal is propagated on to the outward board. Release of relay SIS removes ground from the lower winding of relay GIS which operates to S after one-half second. When relay SI5 operates to S, ground is applied to the top winding of relay SIS over a path from ground through relay SI5 armature and S contact, lower outer front contact and armature relay'i, top winding relay 6I8 to battery. Relay GIB therefore operates and during its operation time the negative battery is temporarily removed from the apex of relay 609. This does not cause relay 492' in Fig. 4to leave its S Contact, however, since the current in the bottom Winding of relay 432 holds it on S. The timed space signal toward the outward board is therefore not inf terrupted. Soon relay 6I8 is completely operated and negative battery is again applied to the apex of relay 69 and the space signal toward the outward board still persists.

A fractional part of a second after relay GIB in the through-cord is operated, relay 436 in the interofce trunk toward the inward board releases, since the space signal sent out from the inward board has been long enough to cause it to release.

Release of relay 406 causes relay 484 to release. With relay 4534 released, ground is applied to the ring of plug 623, causing relay 6 I 9 in the throughcord to operate. With relay 404 released, negative battery is applied to the apex of relay 4t2 and relays BIS and SID in the through-cord reoperate to M. The reoperation of kthese relays will not cause the spacing signal sent tov/ard the outward board to be interrupted, however, since relay SIB which was previously operated now has control of this signal and with relay GIB now operated relay 6I8 remains operated, even though relay SI5 again reoperates under control of relay BIS.

As explained above, the timed space signal sent from the inward board is not broken at the through-switchboard, due to release of relays 405 and 404 in the through-inward interoce trunk terminating circuit. This space signal therefore is long enough to allow relays 496, 4M and 465 in the interoice trunk at the outward board to release. With relay 494 released, ground is applied to the ring of plug in the outward cord. This ground causes relays 2I5 and 2I4 to operate and cord lamp 225 to light, as heretofore explained.

A fraction of a second later, relay @Il in the inward cord operates to S, causing relay i518 to release and a marking signal to be reestablished on the trunk. This signal causes the ground to be removed from the ring of plug 22% at the outward board. Relay 2I5 therefore releases, but current through the lower winding of relay 2I4 holds it operated and Ell I. P. M. ground is therefore now connected to lamp 225 and it ashes, giving the outward operator an indication that the called subscriber has recalled.

The reestablishment of this marking signal on the trunk at the inward board, which ultimately causes the flashing at the outward board mentioned in the preceding paragraph, is started when relay 6l1 operates to S under control of its top winding. When relay 6I1 leaves its M contact, the locking circuit through the lower winding of relay 6l0 is broken `and relay 6|8 releases, because relay 6I9 is at that time released, as the calling subscriber has completed the operation of sending the recall signal. Release of relay 6l8 removes negative battery from the apex of relay 609. Previously when the called station loop was reclosed, relays 610 and 6 I6 were operated to M. With relay 6I6 operated to M, relay 6|6 operated to M and relay 626 operated to M. Positive battery is therefore applied to the apex of relay 609, through the M contact of relay 6I0, armature and front contact of relay 626 and the lower outer back contact and armature of relay 6l8.

Relay 609 in the inward cord remains on M when positive battery is applied to its apex, but relay 402' in the inward through-cnice trunk terminating circuit connected to plug 622 of the inward cord operates to M, causing negative battery to be applied to the top winding of relay 4H (Fig. 4). Relay 4H operates toM and relay 412 at the through-olmos: then operates to lVl'. With relay 4I2 on M, relays 401 and 406 at the through-office operate to M. Relay 404 then operates and removes ground from the ring of plug 623 of the through-cord. Relay 6I!! in the through-cord then releases, causing relay 6l8 to release immediately. As soon as relay 6I8 releases, positive battery is again applied to the apex of relay 609, through the M contact of relay 6 l ll, make contact of relay 626 and lower outer back contact and armature of relay 6l8.

In the interolfice trunk toward the outward board (Fig. 4) relays 402 and 4I l at the through-cnice and relays 412, 401 and 406 then 4operate to M. Relay 404 at the outward oilice reoperates. removing ground from the ring of plug 226 (Fig. 3) and releasing relay 2l5. The cord lamp then ashes as pointed out above.

Upon noting the flashing cord lamp the outward operator answers the recall by operating the typing key, T, to associate the position teletypewriter circuit with the cord. This operation causes relay 205 to operate, removing ground from the top winding of relay 2I4. Relay 214 therefore releases and lamp 225 is extinguished. Relays 226 and 22|, however, remain operated, as sleeve relay 2l 9 is still operated.

L. Outward operator recalls and inward operator answers recall The outward operator may send a recall signal to the inward operator by momentarily operating the send-recall key, RCL, in the outward cord. The answering cord lamp at the inward board flashes. The corresponding answering cord lamp at the through board does not flash. The inward operator answers the recall by operating the typing key and challenging. Operation of the typing key extinguishes the flashing cord lamp. Reference to Figs. 2, 3, 4 and 5 shows this operation.

When the send-recall key, RCL, in the outward cord, Fig. 3, is operated momentarily, relay 2l1 is operated over a circuit from battery through the lower outer armature and front contact of relay Elli, M contact and armature of relay 216, contacts RCL key, lower winding of relay 2H to ground through the upper outer front contact and armature of relay 204.' Operation of relay 2H cuts and closes the transmission circuit toward the top winding of relay 2l2 to negative battery through the right-hand armature and front contact of relay 2|3. It also causes the transmission lead to the tip of plug 226 to be opened. As soon as relay 2H operates, it is held operated through its upper winding under control of the M contact of relay 2l6. Operation of relay 2I1 also removes ground from the lower winding of relay 2 i6. This causes condenser 234, also connected to this winding, to charge. After 11A; seconds, this condenser is charged, and relay 26 then operates to S under control of its top winding. Relay 2I1 is then released and the transmission circuit to the tip of plug 226 is again closed. The recall signal is therefore a timed open signal of about 11/8 seconds duration.

When the transmission lead is opened at the beginning of the recall, relay 402, Fig. 4, connected to plug 226, operates to S under control of its lower winding and then relay 4H in the outward oflice and relays 4I2 and 401' in the through-office operate to S. The spacing signal is then transmitted through plug 622 to relay 600 in the through-cord. Relay 669 operates to S` under control of its lower winding and applies negative battery to the tip of plug 623, which causes relays 402, 4H, 4t2' and 401 in the through inward trunk, and relay 609 in the inward cord, to operate successively to S. The 406 relays in the trunk circuits at the through and inward boards, respectively, operate to S one second after their associated relays operate to S. When the 466 relays operate to S, the corresponding 464 relays release and cause ground to be applied momentarily to the rings of plugs 622 at the two switchboards. With ground applied to the rings, the respective 601 relays in the through and inward cords operate over a path from ground through the upper inner armatures and front contacts relays 404, rings of jacks 408', rings of plugs 622, lower inner break contacts relays 604, winding of relays 661, upper inner break contacts of relays 604, lower front contacts and armatures relays 606 to battery. Operation of relays 601 causes relays 606 to operate over a path from ground through the upper armatures and front contacts relays 661, relays 606 windings, to battery. Operation of relays 601 momentarily opens the circuits from battery through the lower armatures and front contacts relays 606, windings relays 606, upper back contacts and armatures relays 601 to ground. Relays 606 do not release, however, as they are slow-release relays and relays 661 do not remain operated long enough. This is so because, although the transmission circuit was opened for approximately 11/8 seconds, the 406 relays required approximately one second of this period to operate to S and release the 604 relays. When the transmission circuit closed approximately 1/8 second later. the 406 relays operate to M without appreciable delay reoperating relays 404. The time during which relays 404 are released and lground is furnished for the operation of relays 601 therefore is limited to 1/8 second. This is not suiicient for the release of relays 606.

As has been explained, heretofore, relay 612 is operated at the through-cord and is not operated at the inward cord due to variations in the resistance between the sleeve circuit to which plug 623 is connected in the two cases. At the throughboard, therefore, operation of relay 661 does not light lamp 62| because relay 612 is operated and the lamp circuit lis opened at the upper inner back contact and armature of relay SI2. At the inward board, however, lamp 62| is lighted and the night-alarm relay 625 is energized.

After release of the 501 relays, the 608 relays remain locked up to ground through their lower make contacts over a path from battery through relays E08 windings, lower front contacts and armatures relays 608, lower outer armatures and front contacts relays 6|3, upper inner armatures and front contacts relays 695, to ground. At the inward board, the 62| lamp now flashes over a circuit from ground through interrupter 028, upper armature and front Contact relay 608, upper back contact and armature relay 6|2, nlament lamp 02|, winding relay 625, to battery. The night-alarm relay 625 is operated intermittently until the operator answers the recall.

Upon noting the flashing cord lamp, the inward operator operates the typing key, T, to associate her position circuit with the cord and then challenges. Operation of the typing key operates relay SIE, breaking the holding path of the flashing recall relay 508, releasing the relay and eXtinguishing lamp 62 Since the through operator did not receive a hashing recall lamp, she does not operate her typing key, T, and relay 690 in the through cord remains operated until plug 022 is disconnected and relay 605 releases.

M. Splitting and ring-answering keys The split SP key in the outward cord Fig. 3 and in the through and inward cord Fig. 5 is provided to enable the operators to associate the position teletypewriter with either end of a cord, while providing the proper battery condition for both ends of the cord.

In Fig. 3 operation of the right-hand portion of the key associates the printer with the calling end of the cord. The circuit may be ltraced from negative battery, upper right-hand armature and make contact of the split key, teletypewriter contacts, break key, upper winding relay 39|, upper left-hand break contact split key, conductor 239, upper inner armature and iront contact of relay 205, winding of relay 209, top winding relay 2| armature and M contact relay 2 l 2 to positive battery. Relay 2| follows the teletypewriter signals which are repeated over the tip circuit of the calling cord.

Operation of the right-hand portion of the split key also furnishes positive battery through its lower front contact and armature, break contact of the ring-answering-cord key, conductor 229, upper outer m'ake-before-break contact of relay 205, upper middle front contact and armature relay 204 to the tip of the answering cord.

Operation of the left-hand portion of the split key, Fig. 3, associates the teletypewriter with the tip of the answering cord over a circuit from positive battery, left-hand lower make contact and armature split key, upper winding relay 30|, break key, teletypewriter contacts, upper outer right-hand break contacts split key, upper break contact ring-answering-cord key, conductor 229, upper outer make-'before-break contact of relay 205.

Operation of the left-hand portion of the split key also furnishes negative battery to winding of relay 299, through the split key left-hand upper armature and make contact.

The split key circuit and operation in Fig. 5 is practically identical with that in Fig. 3 and its detailed description is therefore not repeated.

In Fig. 3 a key is provided to enable an outward operator to ring on an answering cord. Operation of the ring--answering-cord key RA furnishes ringing current through its lower front contact and armature to conductor 229 and thence to the tip of the answering cord. At the same time negative battery is again furnished through its upper armature and make Contact, upper righthand break contact split key, teletypewriter contacts, break key, upper winding 30|, upper lefthand break contact split key, conductor 230, upper inner armature and front contact of relay 205 to winding of relay 209.

N. Subscribers disconnect In order to disconnect, the subscriber at either station operates the power switch tothe left or off position. The motor stops and the associated corp lamp at the outward switchboard burns steadily.

When the calling subscriber operates the power switch Fig. 2 to the left or off position the teletypewriter motor stops and relay ||8 is released. Relay |0| operates and remains operated over a circuit from negative battery, resistance H4, lower winding relay |0| inner make contact and armature relay |03, resistance ||2, lower back contact and armature relay H8, upper armature and back contact relay ||8 to ground. Ground is connected through the armature and front contact of relay |0| to the ring of jack |04. Relay 201 in the outward cord, Fig. 3, operates from this ground through ring of plug 224, upper inner armature and front contact of relay 204, lower outer armature and back contact, relay 208, relay 201 winding, to battery. Operation of relay 201 operates relay 203 over a circuit from battery through the lower winding relay 208, upper inner armature and front contact relay T, lower outer front Contact and armature relay 208, upper inner back contact and armature relay 204 to the same ground on the ring of plug 224. Relay 208 locks from battery through its upper armature and front contact, lower armature and front contact relay 205, to ground. Cord lamp 223 lights from ground through the lower inner front contact and armature relay 20|, filament lamp 223, winding relay 222, to battery. Operation of relay 201 also applies negative battery through its lower outer armature and front contact to relay 2|| winding. Relay 2|| is held operated and relay 2|| holds relay 209 on M.

When the called subscriber operates his power switch to the left relay ||8 releases and ground is applied to the ring of plug 623 of the inward cord. Relays 6|9 and 6|8 are operated over circuits heretofore described. Since in this case the ground is left permanently on the ring of plug 623, relays 6|'9 and 6|8 remain operated whereas when a recall signal was sent, relay 6| 9 was operated for only a short interval and relay 6| 8 remained operated only during the release time of relay 6H.

A permanent spacing signal is sent over the trunks to the outward board as soon as relay E18 operates. After approximately one second, relay 406 in the interoice trunk circuit at the outward board operates to S and relay 404 then releases. Release of relay 404 applies ground to the ring of jack 226 and relays 2|5 and 2|4 operate from this ground. With relay 2|5 operated, lamp 225 is lighted indicating to the outward operato;- that the called subscriber has disconnected.

O. Outward operator disconnects To disconnect, the outward operator pulls ydown both cords. The answering cord lamps at the through and inward board light. The trunks between each pair of switchboards become idle and may be used for new calls even though the inward and through operators have not disconnected their cords at the respective oirices.

When the outward operator removes plug 224 from the calling station line, relays 20|, 202, 204 and release.` Release of relay |03 restores the station line circuit to the normal idle condition. Release of relays 20|, 202 and 204 in the outward cord causes the 201 and 208 lamp relays to release and the-223 lamp is extinguished. The transmission circuit through the 200 and 2|| relays is held closed, however, since when relay 204 releases, negative battery is connected from the left-hand outer armature and make contact of relay 2|0 through the break contact of the make-before-break combination of relay 204 top winding of relay 2||, armature and M contact relay 2|Z to positive battery. The trunks toward the through and inward boards` are, therefore, held closed.

When the outward operator removes plug 220 from the interofilce trunk jack 408, relays 2|0 and 40| release. Release of relay 2|9 in the outward cord causes all relays in the cord to restore to the idle condition and lamp 225 is extinguished. Release of relay 40| in the interoice trunk causes the current through the bottoni winding of relay 400 to be reduced since the shunt around resistance 4|3 is removed. On the basis that a disconnect signal had been received from the called station and since the circuit through the upper winding of relay 402 was open when the plug was removed, this reduced current is sufficient to 0perate relay 402 to S and the S signal is started Y over the trunk toward the through board. Release of relay 40| also` removes ground from the bottom winding of relay 403 and condenser 4|4 associated with the bottom winding starts charging. Relay 403 remains operated for about 11/2 seconds to guard the trunk from becoming idle. If the called subscribers disconnect had been received before the outward operator pulled down the connection, relays 401 and 400 would be on S, relays 404 and 405 would be released.

The spacing signal sent over the trunk to the through and inward switchboard causes the 401 relays on the answering side of the connection at these points to release. One second after the release of these respective relays, the associated 400 relays release, causing the 404' and 405' relays to release. Ground is then applied to the ring of the answering cords, causing relays 601 to operate and relays 600 to start releasing. After about second the 606 relays release. Whenrelays 006 release, relays 604 operate over path from battery through relays 604 windings, disconnect lamp release key contacts, armature and back contacts relays 000, upper inner armature and front contacts relays B05 to ground. The 004 relays in both cords are locked over a circuit from battery through relay 004 windings, disconnect lamp release key, D.L.R., contacts,

" upper outer fron-t contacts and armatures relays 004 to ground. When the 004 relays operate, relays 00| and |502 in bothcords Vare released. Release of relays 60| releases relays 605. Release of relay 605 releases relay 608 `and relay SI2 in the through cord and relays 6|| and 620 in both cords. Relays 600 and 0|2 in the inward cord were already released as heretofore explained. Lamps 02|in both through and inward cords light from ground through the lower, armatures` and front contacts of relay 00T, iback contacts and upper armatures of relay GIR, filaments of lamps 62|, relays 625 windings to battery. When relays 604 operate and relays 600 and. 020 release in both through and inward cords, the tip, ring and sleeve connections on both sides of each cord are disconnected from the trunks. The inward and through operators upon noting the lighted lamps in `each respective case, pull down both cords and extinguish the lamps by momentarily depressing the disconnect-lamp-release keys D.L.R., which open the locking circuits of relays 004 and 001.

At the outward board, a fraction of a second after the through and inward cords are automatically disconnected, relay 403, whose release was started when the cord at the outward board was pulled down and relay 40| released, finally operates to S and the trunk is made idle at that board.

At the through board, the trunk toward the inward board is held busy for slightly more than one second after the cord at the through board was automatically disconnected, since the ground was not removed from the lower winding of relay 400 until that time. In either case the trunk tol the outward cord at the through oiiice 4and the trunk to the through board at the inward oiiice may be seized before the 403 relays at the outward and through boards, respectively, have operated to S, but `the idle indicator under control of the 400 relays holds the trunk busy at the outward and through oiices, respectively, until the 403 relays have released, This arrangement prevents the trunks from being seized before disconnect signals have registered at the same time releasing them immediately thereafter.

P. Disconnect in error In case an operator pulls down a cord from a busy trunk in error after a connection has been` fully established, the corresponding trunk lamps in the multiple will ash rapidly indicating to the operator that she has broken the connection. She may then restore the cord without requiring the connection to be completely built up again. At the through board pull down of the answering cord will cause the trunk lamps associated with both cords to ash even though the calling cord is still plugged up.

Referring to Fig. 4, when a connection is es tablished relays 403 and '400 are on M and reu lays 40|, 404 and 400 are operated. Relays 402 and 40'! may be on M or S depending on the direction of transmission of communication signals and whether the particular component part of each teletypewriter character is a marking or spacing signal. 1n any event the 407 relay reu mains on its marking contact an insurlicient length of time for relay 400 to remain on M as was heretofore explained. Under this condition if a cord is removed from jack 400, relay 40| releases, but since relays 404 and 400 remain operated, a source of interrupted battery is applied through the upper inner make contact of relay 405 through lamp 400, ilament to ground, and the lamp flashes. Relay 402 is now under control of relay 4|2 since ground is applied to the tip of jack 40B through the lower back Contact of relay 40|, upper outer make contact relay 405 and resistance 4|5. The current to this circuit through the upper winding of relay 402 from battery at relay 4|2 M contact, in a direction to hold relay 402 on M as long as relay ME is on M and to release 402 to S when M2 is on S. A false disconnect signal is therefore prevented from being sent over the trunk as long as relay 4t2 is not on S more than one second. Furthermore, relay 462 repeats the signals from relay 4t2 back over the circuit to relay 4l i giving an indication of trouble to a sender, if at that time teletypewriter signals are being transmitted in a direction to operate relay M2.

Upon noting the flashing lamp the operator restores the cord, relay 40| operates and 4the connection is reestablishe'd.

2. LocAifTo-Lociir CoNNnc'lrcN In a local-to-lccal connection, a cord circuit per Fig. 3 is used in conjunction with two Figs. 2 as indicated in the diagrams per Fig. 1 and Fig. 1A. The operation Will not be described in detail here 'as it is very similar to the operation of the same gures in the case of the built-up connection described under 1 above.

S. Dira/sr INTERoFrioE Connection' In a direct interoiiice connection, Figs. 2, 3, 4, 5 and 6 are used as indicated in Fig. l and Fig. 1A. The operation will not be described in detail here as again it is very similar to the operation of the same figures in the case of the built-up connection described under l above.

What is claimed is:

1. In a manual telegraph system, a first manual telegraph central switching station, a second manual telegraph central switching station, a local telegraph station individual to each of said central stations, means for establishing a continuous telegraph path connecting said stations, a. telegraph repeater in said path, signal and control means in the path at each station for establishing said path by the straightforward me'thod with full through supervisory control localized in the iirst central station.

2. In a telegraph system, a iirst manual telegraph central switching station, a second manual telegraph central switching station, a local telegraph station individual to each oi said central stations, at least one manual telegraph central switching station intermediate the first central station and the second central station, means for establishing a continuous telegraph path connecting said stations, a telegraph repeater in said path, signal and control means in ,the path at each station for establishing said path by the straightforward method with full through supervisory control localized in the iirst central station.

3. In a telegraph system, telegraph exchanges,

, each comprising a sufbscribers line and an operators position, means comprising an operators cord in each of the exchanges, and a telegraph channel between said exchanges for transmitting messages and `supervisory signals from one to the other of said exchanges, and means comprising said operators cords and another telegraph channel between said exchanges for transmitting messages and supervisory signals from said other to said one of the exchanges.

4. In a telegraph system, a rst telegraph exchange comprising a calling subscribers line, a second telegraph exchange comprising a called subscribers line, two telegraph channels between said exchanges, an opera'tors cord in the fir-st exchange connecting said calling line to said channels, and an operators cord in the second exchange connecting said channels to said called line, means in the iirst exchange for transmitting signals over one of the channels and means therein for receiving signals over the other of the channels, means in the second exchange for receiving signals over said one and means therein for transmitting -signals over said other of the exchanges.

5. In a manual Iteletypewriter exchange system, a first central station, a second central station, a plurality of local stations associated with each central station, a telegraph line circuit connecting each local station with its associated central station, at least one central station intermediate the first central station and the second central station, a telegraph path connecting any line circuit associa/'ted with the rst central station with any line circuit associated with the second central station through the intermediate central stations in tandem, means for establishing the path by the straightforward meth-od and instrumentalities for full through supervision localized at the originating central station.

6. In ya. telegraph system, the combination of a rst central station, a second central station, a full duplex telegraph path connecting the central stations comprising a cord circuit at each station and a telegraph trunk between stations, supervisory signal means in the cord circuits, relay means Tin the trunk circuits for discriminating between signals transmitted over the trunk on the :basis of their duration for controlling the cord circuit supervisory signals in diiTerent manners for signals of different duration.

7. In a telegraph system, a first central station, a second central station, at least one central station intermediate the first central station and 'the .second central station, a full duplex telegraph path between lthe first central station and the second central station .through the intermediate central stations comprising a cord circuit at each 'central station and a trunk cir-cuit between each central station in tandem, supervisory signal means in the cord circuits, relay means in the trunk circuits for vdiscriminating between supervisory signals transmitted over the path on the basis of their duration, and means `for controlling the cord circuit supervisory signals according to the discrimination.

8. In a manual straightforward telegraph system with full through supervision, the combination of a first central station, a second central station, a plurality of local `stations associated with each central station, a continuous telegraph path connecting any local station associated with the rst central station with any local station associated with the second central station through its associated central station, signal means in the path at each station, relay means in the path, responsive to control means at either local station for stopping the transmission of communication signals ever the path without operating Ithe signal means in the path.

9. In a manual straightforward telegraph system with through supervision, the combination of a first central station, a second central station, a plurality of local stations associated with each central station, at least one central station intermediate the first central station and the second central station, a telegraph path connecting any local station associated with the rst central station With any local station associated with the second central station through the central stations in tandem, signal means in the path, means in the path responsive to control means at either local station for stopping the transmission of communication signals over the path from the other local station without operating the signal means in the path. 

